Vane core assembly for use in making centrifugal elastomer coated impellers

ABSTRACT

An elastomeric-covered shrouded impeller having a pair of disk-like shrouds enclosing vanes and vane passages which has an improved throat opening having sweeping internal sidewalls is disclosed. A three-piece mold core is utilized to form the vane passage and the sweeping curved throat inlet of the impeller.

This application is a continuation application of Ser. No. 845,976,filed Mar. 31, 1986, now issued as U.S. Pat. No. 4,732,541, which was adivisional application of Ser. No. 743,067 filed June 10, 1985, and nowissued as U.S. Pat. No. 4,706,928.

BACKGROUND OF INVENTION

1. Field

The instant invention relates to elastomeric-covered shrouded impellersfor centrifugal pumps.

2. Prior Art

Shrouded impellers in which the vanes and vane passages are enclosedbetween a pair of opposed shrouds or disks are relatively commonplace incentrifugal pumps. Shrouded impellers are available in both metal andelastomer-covered metal constructions. Metal impellers are typicallyutilized in non-abrasive, non-corrosive environments. Elastomer-coveredimpellers, because of expense and difficulty in making same, aretypically utilized only where abrasive or corrosive resistance isrequired, for example, in slurry pumps handling abrasive or grittysolids in a liquid media or in dealing with corrosive liquids such asacids and the like.

An elastomeric-covered impeller is formed about a metal insert. Thetechnique involves placing the metal insert within a mold and providingcore elements which provide for the voids within the impeller aftermolding. Elastomeric material is forced generally under pressure intothe molds so that those spaces which exist between the metal insert andthe core elements are filled with rubber thereby forming theelastomeric-covered shrouded impeller.

A typical rubber-covered impeller is shown in FIG. 1 in an elevationalview showing the peripheral edge of the impeller with vane passageopenings shown at the periphery. The formation of the throat opening andvane passages in the molding process is relatively straightforward inthis type of construction.

An elevational view of the vanes of a shrouded impeller along sectionlines 2--2 of FIG. 1 is illustrated in FIG. 2. The spacing betweenadjacent vanes is closer near the center of the impeller than around theouter edges of the vanes. In the orientation of the impeller illustratedin FIG. 2, the rotation of the impeller is counter-clockwise.

In the arrangement illustrated in FIG. 3, the vane core, which is aportion of the mold which forms the vane passage, has a uniform width"w" between the inner walls of the front and rear shroud. For thepurposes of description herein of shrouded impellers, the front shroudis the shroud containing the inlet opening in the throat of theimpeller. Thus, the vane core may be easily extracted by a forceperpendicular to the central axis of the impeller.

A slight variation to the arrangement illustrated in FIG. 3 is thatillustrated in FIG. 4 which is another prior art arrangement. Theillustration of FIG. 4 shows some curvature of the inner walls of thefront and rear shrouds. This wall curvature is to provide a flow channelfrom the inlet throat of the impeller into the vane passage whichprovides a gradual change of direction to accomplish the 90° change ofdirection from axial inlet flow to radial outlet flow. The vane passageof the impeller of FIG. 4 is formed by a pair of vane core members, Aand B whereby, the width W_(A) and width W_(B) of each core member issmaller than the width "b" of the peripheral vane passage width.Extraction of these core members is perpendicular to the central axis ofthe impeller and is in the order of core "A" being first removed andthen core "B" being later removed.

In metal impellers with enclosed vanes the formation of shrouds withcurved inner walls has been practiced for quite some time. Metalimpellers are generally formed by sand casting, whereby the formation ofcurved interior walls of the forward and rear shrouds has been easilyachieved since solid core members are not used in the casting process.Thus, the achievement of a channel connecting the inlet throat with thevane passage in a manner such that the channel encounters no sharp anglerestrictions has been long practiced with metal impellers.

The presence of a right-angle corner such as that present in theconstruction illustrated in FIG. 3 may cause velocity loss as well asturbulence near the square corner and cause erosion of the elastomericcovering on the back shroud in the area directly opposite to the squarecorner on the front shroud.

SUMMARY OF THE INVENTION

A unique elastomer-covered shrouded impeller having a pair of disk-likeshrouds enclosing vanes and vane passages with an improved throatopening has been invented. The throat opening into a particular vanepassage is formed between a front disk-like shroud which has a sweepinginternal sidewall and a rear disk-like shroud having a conicalprojection at its center to form a curved channel which interconnectsthe inlet opening of the impeller with each vane passage so as tointroduce axial inlet flow into the right angle peripheral flow in thevane passages with a minimum eddying effect.

The invention further involves a vane core mold assembly comprising atleast three vane core members to form a vane passage which has anon-uniform width between the interior walls of the front and rearshrouds and particularly where the width adjacent the inlet portion ofthe impeller is substantially greater, often about twice as great ormore, than the width of the vane passage opening at its peripheral edgebetween the front and rear shrouds. The vane passage also has anon-uniform spacing between adjacent vanes whereby the opening at theperipheral edge of the impeller is significantly greater betweenadjacent vanes than the opening between adjacent vanes near the inlet.

Thus, in the instant invention the vane passage is a very irregularvoid, having a lateral width near the center of the impeller which ismuch greater than the lateral width (lateral width being theperpendicular distance between the front and rear shrouds) near theperiphery of the shrouds while the circumferential spacing betweenadjacent vanes is exactly the opposite, with the greater distancebetween adjacent vanes occurring at the periphery of the shrouds and anarrower spacing between adjacent vanes occurring near the center of theimpeller.

To accommodate the irregular three-dimensional vane passage, the vanecore elements are structured to be removed along an extraction surfacebetween adjacent cores perpendicular to and away from the central axisof the impeller. The core elements are flat members which are curvedalong opposed edges to conform (and to form) the curved vanes. Thecurvatures along opposed surfaces of adjacent vanes which form a vanepassage are mating surfaces so that the vane core members, asillustrated hereinafter, may be removed along an extraction path, asviewed from the face of the impeller, which is an arc. Generally, two ofthe vane core elements extend substantially the whole distance from theperiphery of the vane passage to the inlet portion of the vane passage.Generally, the third vane core element does not extend the full radialdistance of the vane passage.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an elevational view of the peripheral exterior of aconventional elastomeric-covered impeller.

FIG. 2 is a cross-sectional view of the impeller of FIG. 1 along sectionlines 2--2 illustrated the curved vanes and vane passages.

FIG. 3 is a cross-sectional view of the impeller of FIG. 1, alongsection lines 3--3 illustrating the flow channel from the inlet throatto the vane passage.

FIG. 4 is a cross-sectional view similar to FIG. 3 of an impeller havingslightly curved shroud walls to provide an improved flow channel fromthe inlet throat to the vane passage.

FIG. 5 is a cross-sectional view similar to FIG. 3 of an impeller of theinstant invention having radially curved shroud walls forming the vanepassage and a cross-sectional view of the core assembly used to form thevane passage.

FIG. 6 is an elevational view of the vane core assembly member of theinstant invention.

FIGS. 7, 8, 9 and 10 are perspective views of an impeller of the instantinvention with vane core members illustrated in sequential steps ofremoval.

FIG. 11 is an elevational view of the peripheral surface of anelastomer-covered impeller of the instant invention.

FIG. 12 is an elevational, facial view of a vane core element of theinstant invention.

FIG. 13 is a plan view of the peripheral edge of the vane core elementsof FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The instant invention involves a unique construction of shrouded,elastomer-covered impellers. Such impellers come in particularly smallsizes, for example, less than about 12 inches in diameter, and areprovided with a channel comprising the inlet throat and the vane passagewhich is essentially curvilinear. Fluid entering the pump enters axiallythrough an opening in the front shroud and, through the centrifugalaction of the pump, parts in a direction perpendicular to the originalaxial flow. The change of direction for fluids in the instant impellersis very gradual and distinctly different from that in existingelastomeric-covered, enclosed impellers.

Theoretically, the curvature of the flow channel formed by the throat(inlet opening) through the vane passage to the peripheral exit for theimpeller would ideally be a 90° arc of a circle. Such a constructionwould, of course, involve an impeller axial depth which was greater thanabout one-half the impeller diameter. While casting of metal impellersapproximating such a construction in sacrifical molds is relativelystraightforward, making a comparable elastomeric-covered shroudedimpeller encounters molding complexities.

In the instant invention, a mold assembly involving a central coremember and a vane core mold assembly of at least three elements isutilized to approximate an ideal flow channel from inlet to dischargefor an elastomeric-covered shrouded impeller for a centrifugal pump.

The technique for making the impellers of this invention and themultiple-element, vane core mold assembly for forming the sweepingchannel connecting the throat and vane passage is unique. Furtherdescription of the instant invention may be facilitated by reference tothe attached drawings.

The unique channel arrangement associated with the instant invention isillustrated in FIG. 5. The throat inlet 10 connects to the vane passage,which in FIG. 5 is occupied by vane core mold members used in moldingthe appropriately shaped vane passage. As illustrated in FIG. 5, a verygradual change of direction occurs between fluid entering the throat andthen changing directions at 90° to exit the vane core passage at theperipheral edge of the impeller.

The vane core passage 11 is formed between the front shroud interiorwall 12 and the interior wall of the rear shroud 13. The curved surfaceof the rear shroud 13 continues below the vane core passage 11 to form acone-shaped projection 14 with its apex at the central axis of theimpeller 15. A steel impeller skeleton is first placed in the moldbefore rubber is injected. In FIG. 5, the steel skeleton shroud members16 and 17, respectively, form the front and rear shroud inserts aboutwhich the elastomer forms to form the elastomer-covered impellershrouds.

The interior wall of the front shroud adjacent to the throat inlet has acurvature as established by radius R. Radius R is generally determinedby the diameter of the impeller and the amount of sweep desired.Furthermore, the curvature of the interior wall of the front shroud maybe described by several different radii having different focal points.

The juncture of the inner wall 12 of the front shroud with the throatinlet wall 18 approximates a curvilinear relationship, that is thecurvature of the inner shroud wall 12 is such that the throat inlet wall18 is substantially tangential to the curved wall 12 at the point ofjuncture.

The interior wall 13 of the rear shroud has a curvature such that at theapex of the cone 14 the curvature of the cone wall is such that anextension of such curved wall joins with the central axis 15 of theimpeller in a curvilinear fashion, that is, the axis is substantiallytangential to the extended curve of the curved wall of cone 14.

The center core plug 19 is substantially cylindrical in shape at thethroat inlet area and has longitudinal grooves circumferentially spacedequidistantly about the plug near the distal end. These groovesaccommodate the formation of extensions of the vanes into the inletthroat and are dished on the end to form the conical projection 14. Thecenter core plug mates with vane core elements A B and C at boundary orparting surface 20. Vane core member A joins at parting line 21 withvane core member B. Parting line 21 is, in fact, a planar surface asillustrated in other drawings, and is substantially perpendicular to thecentral axis 15. Vane core member "A" has a maximum width W_(A), whichmust not be greater than its width at the exit of the vane passage.Since the extraction of the core is in a direction perpendicular to thecentral axis 15 no thickness of any core member can exceed the width ofthe core member at its exit point. The width of W_(A) must, of course,be less than the width of the exit as illustrated by letter "b".Preferably, the width W_(A) is significantly less than the exit width"b". The second vane core member B should have a sufficient thicknessnear its exit to be sufficiently durable that it is not easily broken.For example, if core member A were substantially as thick as exit widthb then core member B may be substantially a knife edge at its upperportions and, therefore, would be easily broken.

In the core mold arrangement illustrated in FIG. 5, the width of W,which is the combined widths of core members A, B and C, is greater thanthe exit width "b". In the case of core member B the width W_(B) is notthe maximum width of the element, however, the maximum width of coremember B, which is near shoulder "X", must be smaller than the exitwidth "b". Core members B and C are formed with a shoulder "X" so thatagain a silver or knife edge is not required on core member C.Structuring core member C such that it is recessed slightly into coremember B makes core member C an easier part to fabricate and assures abetter seal at the sealing surfaces between core members so that themold surface presented to form interior wall 12 is a continuous surface.Core member C and core member B are joined together by pins projectingfrom core member C which are recessed within bores in core member B.Conversely, the pins could be affixed to core member B and the boresrecessed within core member C. Since the surfaces at the joint betweencore members B and C are generally machined surfaces the parts may tendto stick together after being subjected to the pressures within the moldduring injection of the elastomeric rubber material. A pry slot 26 isprovided for insertion of a screw driver or the like, to pry the cores Band C apart. Also air injection port 27 is provided in core member B sothat air pressure may be introduced into bores 24 and 25 to eject pins22 and 23 to separate cores C and B. Pry slot 26 and air injection port27 are at a boundary surface between cores B and C and the center coreplug so that the elastomer in liquid form, as it is filling the mold,cannot reach the slot 26 or port 27, so that these remain open andunfilled with rubber.

A frontal or elevational view of core member C is illustrated in FIG. 6.Core C has a substantially crescent shape; the central circle 28illustrating the cylindrical wall of throat 10. FIG. 6 illustrates thecentral core plug 19 positioned in place with grooves 29 in the distalcylindrical surface of the plug spaced so as to form the interior tipsof the vanes which protrude into the throat region. Thus, core member Cat surface 30 forms a portion of the surface of a vane 31 while thesurface 32 of the core C forms a surface of a vane 33. The juncture line"X" is illustrated showing a juncture surface between core B and core C.Surface 34 is the parting surface formed between core C and the centralcore plug 19. Pry slot 26 is shown in dotted lines as is injection port27 which interconnects bores 24 and 25.

FIGS. 7, 8, 9 and 10 illustrate sequentially the removal of vane coremembers A, B and C and central core plug 19.

FIG. 7, is a perspective view of an elastomeric-coated impeller whichhas been molded and which has had the center core plug 19 removed. Also,two of the vane passage core subassemblies have been removed. In moldinga complete impeller with three vanes, and three vane passages, threevane core subassemblies similar to the subassembly shown in FIGS. 7through 10 are utilized so that three vanes are formed and three vanecore passages are formed in the impeller. In FIG. 7, cores A, B and Care still positioned within the impeller. In FIG. 8, vane core A hasbeen removed. Core A has a rim 34, which is substantially as thick atits outer edge as the vane passage of the impeller. A quarter-circlearc-like shoulder 35 is formed in the rim 34, said shoulder having athickness substantially the same as the thickness of the rim 36 of vanecore "B". Thus, vane core "A" and vane core "B" mate in concentricfashion as well as in a planar fashion where the tongue 37 of vane coreA extends into the vane core passage.

In FIG. 9, vane core B is shown after it has been removed from theimpeller. Vane core B has an outer rim 36 which is a third of a circlein its arc and mates with the third of a circle shoulder 35 of vane coreA. Vane core "B" has a tongue 38, which extends into the vane corepassage. The edge surfaces of tongues 37 and 38 are illustrated in FIG.5 and the tongues have a width, W_(A) and W_(B), as indicated in FIG. 5.

FIG. 10 shows vane core C removed from the impeller. The substantiallycrescent-shaped vane core C is illustrated.

It is apparent from FIGS. 7 through 10, that similar vane core elementscould be utilized to form any number of vane passages and vanes in anenclosed shrouded impeller. For example, an impeller could be formedhaving three, five, six, or any number of vanes and vane passages inwhich the rim portions of the cores A and B, respectively, would beone-third, one-fifth and one-sixth of a complete circle.

A facial view of core elements B and C is presented in FIG. 12. Core Band core A substantially have the same overall shape, i.e. core B mayset in with core A. The flat, planar surfaces of core A are parallel toone another while core B has one flat planar surface which mates with aflat planar surface of core A. The other facial surface is a curvedsurface such that the width between opposed faces of the tongueincreases with distance from the rim. The sweep of surface is such thatit continues with the surface of core C.

That edge of core C designated by the numeral 40 is that portion whichmates with the cylindrical center plug of the mold. Edge 41 of thetongue of core B forms one surface of a vane while edge 42 forms asurface of an adjacent vane. The space occupied by the tongue of core Band core C between adjacent vanes is a vane passage.

The view in FIG. 13 is an edge-on, rim view of cores B and C illustratedin FIG. 12. The outer edge 43 of the rim has a certain width, which isthe width also of the tongue member adjacent the rim. The tongue of coreB increases in thickness with distance from the rim, as illustrated inFIG. 13. The joint 44 between core C and core B is at the shoulder jointbetween these two elements. The affect of the shoulder is about the sameas the increase in thickness of the tongue of core B from the rim to theshoulder. Thus, surfaces 40 and 45 are part of core C. The depth of theshoulder 44 and thickness of core B may be viewed in FIG. 5. Thethickness of edge 40 at its junction with shoulder 44 is about the sameas the thickness of edge 41 at its juncture with shoulder 44. The matingsurfaces between cores C and B are flat, planar surfaces which have asubstantially crescent-shaped outline.

In FIG. 11 an edge-on elevational view of an impeller of the inventionis illustrated. The center of gravity of the impeller is shifted towardsthe inlet opening. A consequence of the increased width of the impellerand the shift in the center of gravity is to position the center ofgravity farther from the external bearing supporting the impeller shaft.Also, because of the greater cantilever effects of the impeller upon thebearing, a larger shaft and bearing are generally required.

Elastomeric impellers of the type of the instant invention for a givendiameter impeller will generally weight more, assuming the samethickness of elastomeric covering, than conventional elastomeric priorart impellers. Such increase in weight further would require an increasein shaft and bearing size. Thus, increased shaft and bearing sizesrequired for construction of this type may have led those skilled in theart away from making impellers of the type of this invention.

It has been found, however, that the elastomer-covered impellers of thisinvention provide a significant increase in hydraulic efficiency, asignificant decrease in power consumption and improved impeller lifewhen compared with prior art-type impellers of similar diameters. Thus,a smaller diameter impeller of the instant invention may be effectivelysubstituted for larger diameter impellers of the prior art type, so thatno real increase in shaft size or bearing size actually occurs whendetermined by pump performance.

Molding of elastomer-covered impellers is done under very highpressures, i.e. injection pressures of 1500 psi. to about 2000 psi, withinternal mold pressure spikes of upwards of 5000 psi, to about 6000 psi.Such high pressures require mold elements which are particularly rugged,especially for vane core elements which, in the instant invention, arecantilevered from an external rim member.

Should deflection or displacement of any mold element occur, severaladverse conditions may result, such as:

a. the hydraulic passageways may be distorted and less efficient thandesired;

b. the thickness of rubber deposited in a particular area may be lessthan desired, thereby diminishing the wear resistance life of theimpeller and

c. the balance and dynamics of the impeller may be adversely affected.

Because of these adverse consequences, the various mold elements mustfit securely together and all elements must be sufficiently strong toresist any imbalance in pressure during the molding process.

Elastomer-covered impellers of this invention have pumping efficiencieswhich are significantly improved over previous configurations ofelastomer-covered impellers. For example, small diameter impellers offrom about six inches to twelve inches diameter show improvements ofabout 30% in pump efficiency when compared to other similarly sizedpumps with configurations such as those shown in FIGS. 1 and 2.

Another measurement of improvement for the pumps of the instantinvention is that power requirements to pump a certain volumetric rateof liquid to a certain head is accomplished with significantly lesspower consumption.

I claim:
 1. A vane core assembly for use in forming a vane passage in aninjection-formed, elastomer-covered, closed-shroud impeller, said vanecore assembly comprising:a first core element having a first lengthsized to extend from a central opening in said impeller to a peripheryof said impeller; a second core element detachably mated with said firstcore element, said second core element having a second length sized toextend from said central opening of said impeller to said periphery ofsaid impeller; and a third core element detachably mounted to saidsecond core element by a pneumatically operatable separation meansadapted for detaching said third core element from said second coreelement, said third core element having a length sized to extend fromsaid central opening of said impeller to a location within said impellershort of said impeller periphery, said third length being dimensionallyless than said first length and said second length.
 2. The vane coreassembly according to claim 1 wherein one of said elements defines aslot therein dimensioned to receive a tool for facilitating a priedseparation of said slot-defining core element from a core elementpositioned adjacent thereto.
 3. The vane core assembly of claim 1wherein said first core element and said second core element eachinclude an outer rim mounted thereon, said outer rims being configuredto coact one with another to retain said first core element instationary relation to said second core element.
 4. A vane core assemblyfor use in forming a vane passage in an injection-formed,elastomer-covered, closed shroud impeller, said vane core assemblycomprising:a first core element, sized to extend from a central openingin said impeller to a periphery of said impeller; a second core element,detachably mated with said first core element, said second core elementbeing sized to extend from said central opening in said impeller to saidperiphery of said impeller, and a third core element, detachably mountedon said second core element by a pneumatically operatable separationmeans adapted for detaching said third core element from said secondcore element, said third core element being detachable from said secondcore element by manipulation through said central opening.
 5. The vanecore assembly according to claim 4 wherein said third core elementextends a distance less than a distance between said central opening andsaid periphery.
 6. A vane core assembly for forming an arc-shaped vanepassage between a pair of adjacent vanes in an injection-formed,elastomer-covered, closed shroud impeller, said impeller having an inletwhich communicates with said vane passages, wherein said vane passagehas a peripheral arcual opening having a length substantially greaterthan its central arcual opening length, wherein a width of said centralopening of said vane passage is substantially greater than the width ofsaid vane passage's peripheral opening and wherein said central openingis transposed from a center line alignment with said peripheralopenings, said vane core comprising a first core element, a second coreelement, and a third core element, said first core element and saidsecond core element having planar mating surfaces which aresubstantially coextensive and at least one third core element whichdetachably mates with a portion of a surface of said second core elementwhich is opposed to said surface of said second core element which is incontact with said first core element; said third core element beingadjacent said central opening to said vane passage wherein said firstcore element and said second core element are dimensioned to extendsubstantially from said central opening to said peripheral openingwithin said vane passage; and wherein said third core element isdimensioned to have a length much shorter than a distance between saidcentral opening and said peripheral opening whereby when said vane coreassembly is positioned within said vane passage, said third coreelement, being positioned within said central opening and extending intosaid vane passage, does not extend sufficiently to reach said peripheralopening; said first core element and said second core element beingretractable from said vane passage along an arc-shaped path defined bysaid vane passage, said third core element being detachably secured tosaid second core element by an attachment means configured to beaccessible from said impeller inlet when said vane core assembly ispositioned within said vane passage wherein said attachment means may beaccessed and manipulated through said impeller inlet to effect adetachment of said third core element from said second core elementwhile said second and third core elements are within said vane passageprior to a withdrawal of said second vane core element from said vanepassage.
 7. A vane core assembly for use in forming a vane passagebetween a pair of adjacent vanes in an injection-formed,elastomer-covered, closed shroud impeller, said vane passage having acentral opening proximate an inlet of the impeller, and a peripheralopening proximate a periphery of said impeller, a width of said centralopening being at least twice as large as a width of said peripheralopening and a length of said peripheral opening being substantiallygreater than a length of said central opening; said vane core assemblycomprising:a first vane core element dimensioned to extend substantiallyfrom said central opening to said peripheral opening of said vanepassage; a second vane core element detachably mounted on said firstvane core element, said second vane core element being dimensioned toextend substantially from said central opening to said peripheralopening of said vane passage; a third vane core element, detachablymounted by attachment means on a proximal end of said second vane coreelement; said third vane core element being positionable within saidcentral opening, said third vane core element having a length less thana length of said vane passage, whereby when said vane assembly ispositioned within said vane passage said third vane core element extendsbetween said central opening and a location short of said peripheralopening; wherein said attachment means are configured to be accessiblefrom said impeller inlet when said vane core assembly is within saidvane passage whereby said third vane core element is manually detachablefrom said second vane core element by manipulation of said second andthird vane core elements through said impeller inlet while said secondand third vane core elements are within said vane passage.